U.S. patent number 7,005,636 [Application Number 10/863,547] was granted by the patent office on 2006-02-28 for method and apparatus for manipulating a microscopic sample.
This patent grant is currently assigned to FEI Company. Invention is credited to Hendrik Gezinus Tappel.
United States Patent |
7,005,636 |
Tappel |
February 28, 2006 |
Method and apparatus for manipulating a microscopic sample
Abstract
In the semiconductor industry, microscopic samples are cut out
of substrates for purposes of analysis. In the case of a known
method, a sample to be cut loose out of a substrate is attached to
a sample carrier connected to a manipulator and the sample is cut
loose from the substrate. Subsequently, the sample is fixed to a
TEM grid and completely separated from the sample carrier.
According to the invention, the sample carrier 3 is left in
connection with the sample 1 and the sample carrier 3 is separated
from the manipulator 4. By making the sample carrier 3 connected to
the sample 1 much bigger than the (microscopic) sample 1, and by
manipulating the sample carrier 3, manipulation--with the aid of a
(macroscopic) manipulator--of the microscopic sample 1 attached
thereto becomes easier than manipulating the sample 1 without the
sample carrier 3 attached thereto. In addition, a mechanical
coupling between manipulator 4 and sample carrier 3 is shown, which
enables a great degree of automation.
Inventors: |
Tappel; Hendrik Gezinus
(Casteren, NL) |
Assignee: |
FEI Company (Hillsboro,
OR)
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Family
ID: |
33513462 |
Appl.
No.: |
10/863,547 |
Filed: |
June 8, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040251412 A1 |
Dec 16, 2004 |
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Foreign Application Priority Data
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Jun 13, 2003 [NL] |
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1023657 |
Feb 17, 2004 [NL] |
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1025503 |
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Current U.S.
Class: |
250/304; 250/309;
250/492.1; 250/492.2; 250/492.21 |
Current CPC
Class: |
G01N
1/32 (20130101); H01J 2237/20 (20130101); H01J
2237/28 (20130101) |
Current International
Class: |
G01N
1/28 (20060101) |
Field of
Search: |
;250/309,492.21,492.1,492.2,304 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lee; John R.
Assistant Examiner: Smith, II; Johnnie L
Attorney, Agent or Firm: Scheinberg; Michael O.
Claims
What is claimed is:
1. A method of manipulating a microscopic sample to be extracted
from a substrate, whereby the manipulating movements are conducted
with the aid of a manipulation system consisting of a sample
carrier and a manipulator, which method comprises the following
steps: attaching the sample to the sample carrier and completely
severing the sample from the substrate, and; subsequently applying
a separation to the sample and the manipulator, characterized in
that the separation is applied between the manipulator and the
sample carrier in such a manner that, after applying the
separation, a portion of the sample carrier that protrudes with
respect to the sample remains attached to the sample.
2. A method according to claim 1, whereby the sample carrier has a
rod-like extremity and the location where the sample is attached to
the sample carrier is the rod-like extremity of the sample
carrier.
3. A method according to claim 1, whereby the sample carrier is
formed by an end portion of a supply of wire, and whereby the
separation is applied by separating the end portion of the supply
of wire from the supply of wire.
4. A method according to claim 3, whereby the method comprises
stretching the wire of the supply of wire, at the location of the
separation area where the separation is to occur, in such a manner
that constriction of the wire occurs.
5. A method according to claim 1, whereby the sample carrier is
detachably coupled to the manipulator.
6. A method according to claim 5, whereby the sample carrier is
embodied to carry several samples.
7. A method according to claim 5, whereby the sample carrier is
provided with a unique identification code.
8. A method according to claim 5, whereby the sample carrier is
attached to a flat holder with a hollow in such a manner that the
sample is located within the hollow so as to be substantially free
all around.
9. A method according to claim 8, whereby attachment of the sample
carrier to the flat holder occurs by mechanical clamping.
10. A method according to claim 8, whereby the flat holder is
provided with a unique identification code.
11. A particle-optical apparatus for performing the method
according to claim 3, provided with: a particle source for
producing a particle beam to cut a sample loose out of a substrate;
a manipulator for moving a sample carrier to a position on a
substrate where the sample is to be extracted from the substrate,
characterized in that the particle-optical device is provided with
a supply of wire for the purpose of forming a sample carrier and
that the particle-optical apparatus is provided with severing means
for applying a separation between the supply of wire and an end
portion of the supply of wire for the purpose of obtaining the
sample carrier.
12. Particle-optical apparatus for performing the method according
to claim 5, provided with: a particle source for producing a
particle beam to cut a sample loose out of a substrate; a
manipulator for moving a sample carrier to a position on a
substrate where the sample is to be extracted from the substrate,
characterized in that the manipulator comprises a coupling
mechanism for detachably attaching the sample carrier to the
manipulator.
13. A method according to claim 2, whereby the sample carrier is
formed by an end portion of a supply of wire, and whereby the
separation is applied by separating the end portion of the supply
of wire from the supply of wire.
14. A method according to claim 13, whereby the method comprises
stretching the wire of the supply of wire, at the location of the
separation area where the separation is to occur, in such a manner
that constriction of the wire occurs.
15. A method according to claim 2, whereby the sample carrier is
detachably coupled to the manipulator.
16. A method according to claim 15, whereby the sample carrier is
embodied to carry several samples.
17. A method according to claim 15, whereby the sample carrier is
attached to a flat holder with a hollow in such a manner that the
sample is located within the hollow so as to be substantially free
all around.
18. A method according to claim 16, whereby the sample carrier is
attached to a flat holder with a hollow in such a manner that the
sample is located within the hollow so as to be substantially free
all around.
19. A method according to claim 9, whereby the flat holder is
provided with a unique identification code.
20. A particle-optical apparatus for performing the method
according to claim 4, provided with: a particle source for
producing a particle beam to cut a sample loose out of a substrate;
a manipulator for moving a sample carrier to a position on a
substrate where the sample is to be extracted from the substrate,
characterized in that the particle-optical device is provided with
a supply of wire for the purpose of forming a sample carrier and
that the particle-optical apparatus is provided with severing means
for applying a separation between the supply of wire and an end
portion of the supply of wire for the purpose of obtaining the
sample carrier.
21. Particle-optical apparatus for performing the method according
to claim 8, provided with: a particle source for producing a
particle beam to cut a sample loose out of a substrate; a
manipulator for moving a sample carrier to a position on a
substrate where the sample is to be extracted from the substrate,
characterized in that the manipulator comprises a coupling
mechanism for detachably attaching the sample carrier to the
manipulator.
22. Particle-optical apparatus for performing the method according
to claim 15, provided with: a particle source for producing a
particle beam to cut a sample loose out of a substrate; a
manipulator for moving a sample carrier to a position on a
substrate where the sample is to be extracted from the substrate,
characterized in that the manipulator comprises a coupling
mechanism for detachably attaching the sample carrier to the
manipulator.
Description
The invention relates to a method of manipulating a microscopic
sample to be extracted from a substrate, whereby the manipulating
movements are conducted with the aid of a manipulation system
consisting of a sample carrier and a manipulator, which method
comprises the following steps: attaching the sample to the sample
carrier and completely severing the sample from the substrate, and;
subsequently applying a separation to the sample and the
manipulator.
The invention also relates to a particle-optical apparatus for
performing this method.
Such a method is known from U.S. Pat. No. 6,420,722 B2.
Such methods are principally used in the semiconductor industry,
where samples of microscopic dimensions are removed from substrates
such as wafers so as to make analyses and/or processing steps
possible. Nowadays, such samples have dimensions of the order of
magnitude of 10 .mu.m at a thickness of 100 .mu.m. There is a
tendency towards still further miniaturization of the structures of
interest, and an attendant miniaturization of the samples to be
extracted. The analyses can, for example, be conducted with the aid
of a TEM (Transmission Electron Microscope), SEM (Scanning Electron
Microscope), SIMS (Secondary Ion Mass Spectroscope) or X-ray
analytical apparatus. The further processing steps may, for
example, comprise thinning the sample with the aid of an ion beam
as part of an analysis with the aid of a TEM.
In the case of the method described in the cited patent text, a
sample carrier in the form of a needle is moved on a manipulator to
a position on a substrate where a sample is to be extracted from a
substrate. Before completely severing the sample from the
substrate, the sample is attached to the extremity of the
needle-shaped sample carrier by means of metal deposition.
In U.S. Pat. No. 6,570,170, an alternative method is described for
removing a sample from a wafer and attaching it to a sample
carrier. To this end, the sample is first cut completely loose from
the substrate using a particle beam and is then attached to the
sample carrier. In the case of both known methods, a situation is
achieved whereby the sample is cut loose from the substrate and
attached to the sample holder so that the sample can be manipulated
with the aid of the sample holder.
After completely cutting the sample loose with the aid of a
particle beam, the sample attached to the manipulator is brought to
another position with the aid of the manipulator.
The sample is subsequently fixed to a carrier in the form of a TEM
grid with the aid of metal deposition. The TEM grid has hollows and
the sample is attached to the edge of such a hollow. After affixing
the sample to the TEM grid, the separation between the manipulator
and the sample is applied by employing an ion beam to cut loose the
metal deposition connection between the sample and manipulator.
A TEM grid consists of a metal foil in which hollows are created
that are bordered by bars of said metal. It usually has an external
diameter of the order of magnitude of 3 mm, hollows of 15 .mu.m or
larger, bordered by bars with a width of 10 .mu.m or more and a
thickness of 10 .mu.m or more. Depending on the chosen embodiment
of a TEM grid, the hollows may be up to hundreds of .mu.m in
size.
A disadvantage of the known method is that the sample mounted on
the sample carrier has to be positioned with sub-micron accuracy on
the TEM grid by the manipulation system, so as to connect the
corner points of the sample to the edge of the hollow without
hindering the spatial accessibility of the sample during further
processing and/or analysis. In this respect, it is important to
realize that the sample has a size comparable to or smaller than
the width of the bars of the TEM grid.
Another disadvantage of the described method is that it does not
offer the possibility of processing or analyzing the sample in
apparatus that requires another grid or holder than that on which
the sample is affixed.
A further disadvantage lies in the determination of the position of
the sample on the TEM grid, whereby, somewhere on the TEM
grid--with a size of the order of magnitude of 3 mm and with
hundreds of hollows--the microscopic sample--with a size of the
order of magnitude of 10 .mu.m--is fixed to a bar.
The invention aims to provide a method that better facilitates
manipulation of the microscopic sample.
To this end, a method according to the invention is characterized
in that the separation is applied between the manipulator and the
sample carrier in such a manner that, after applying the
separation, a portion of the sample carrier that protrudes with
respect to the sample remains attached to the sample.
By making the sample carrier substantially larger than the
microscopic sample and by manipulating the sample carrier,
manipulation--with the aid of a macroscopic manipulator--of the
microscopic sample attached thereto becomes easier than
manipulating the sample without the sample carrier attached
thereto.
When mounting the sample on a TEM grid, with hollows much bigger
than the sample, one achieves a substantial reduction in the
necessary positioning accuracy, and an attendant increase in the
ease of manipulation, if the sample carrier is manipulated in such
a manner that the sample is located in its entirety within a hollow
and the sample carrier thereby rests on one or more bars of the TEM
grid.
Remounting of the sample can occur by release, manipulation and
mounting of the sample carrier, which is easier and more effective
than release, manipulation and mounting of the microscopic sample.
Such remounting may be necessary so as to change the position or
orientation of the sample in the case of initially erroneous
placement, or so as to mount the sample on another grid or another
holder for use in apparatus in which the sample is to undergo
subsequent processing or analysis.
Finally, positional determination of the microscopic sample
attached to the (relatively large) sample carrier is easier than
positional determination of the sample without sample carrier: one
first determines the position of the sample carrier and one then
localizes the sample attached thereto by following the form of the
sample carrier.
In a preferential embodiment of the method according to the
invention, the sample carrier has a rod-like extremity and the
location where the sample is attached to the sample carrier is an
extremity of the sample carrier. An advantage of this embodiment is
that visibility at the location where the extremity of the
relatively large sample carrier is attached to the microscopic
sample is blocked as little as possible by the sample carrier
itself, as a result of which the positioning of the extremity of
the sample carrier upon the sample to be removed, before the sample
is cut loose, is made as simple as possible.
In a further embodiment of the method according to the invention,
the sample carrier is formed by an end portion of a supply of wire,
and, in this scenario, the separation is applied by separating the
end portion of the supply of wire from the supply of wire. An
attendant advantage of this embodiment is that the remaining end of
the supply of wire can--in the case of repeated application of the
method--now be used as a new end portion of a subsequent sample
carrier. In this scenario, separation can comprise stretching the
wire of the supply of wire in such a manner that constriction of
the wire occurs, which has the advantage that the newly formed end
of the supply of wire has a smaller diameter than the rest of the
sample carrier, which simplifies placement of that end upon the
microscopic sample to be removed.
In another embodiment of the method according to the invention, the
sample carrier is detachably coupled to the manipulator. An
advantage of this embodiment is that the manipulator--in an
automated manner, and thus without human intervention--can remove
the sample carrier from, for example, a cassette and, after
attachment of the sample to the sample carrier and cutting loose of
the sample, can place and release the sample carrier with attached
sample into the same or another cassette, after which this cassette
can be removed from the apparatus in which this method is
performed, so as to allow the samples present in the cassette to
undergo processing and/or analyses. The sample carrier can have a
form that is suitable for use in apparatus for performing analyses
and/or processing subsequent to extraction of the sample. The
sample carrier can be embodied to hold multiple samples, which can
shorten the time necessary for analysis and/or processing. It is
also possible to provide the sample carrier with a unique
identification code, which simplifies identification of the sample
during subsequent analyses and/or processing. This embodiment of
the apparatus is principally advantageous in environments where
large numbers of samples are analyzed, such as in production
environments for integrated circuits.
The invention will be elucidated on the basis of figures, in which
identical reference symbols indicate corresponding elements.
Although the figures only explain the method by means of which the
sample carrier is attached to the sample before the sample is cut
loose from the substrate, it is just as possible to first cut the
sample fully loose before attaching the sample to the sample
carrier.
To this end:
FIG. 1A is a schematic depiction of a wafer with a sample that is
partially cut loose;
FIG. 1B is a schematic depiction of a transverse cross-section from
FIG. 1A of the wafer with the partially cut loose sample;
FIG. 2 is a schematic depiction of a manipulator system with a
wafer;
FIG. 3 is a schematic depiction of a wafer with a partially cut
loose sample to which a sample carrier is attached;
FIG. 4 is a schematic depiction of a manipulator system with a
sample attached thereto in which the cutting loose of sample
carrier and manipulator is occurring;
FIG. 5 is a schematic depiction of a TEM grid upon which is located
the sample carrier with sample attached thereto;
FIG. 6 is a schematic depiction of a manipulator system in which
the sample carrier is formed by a supply of wire;
FIG. 7A is a schematic depiction of mechanical separation means
such as can be used in FIG. 6;
FIG. 7B is a schematic depiction of mechanical separation means
such as can be used in FIG. 6;
FIG. 8A depicts a detachable sample carrier;
FIG. 8B depicts a manipulator with mechanical holding means for
manipulating a sample carrier as shown in FIG. 8A;
FIG. 9 depicts a detachable sample carrier embodied for attachment
to a flat holder;
FIG. 10 shows a flat holder to which the sample carrier of FIG. 9
is attached.
FIGS. 1A and 1B show a substrate 2 in the form of a wafer
containing a partially cut loose sample 1. The cutting loose of the
sample can occur in a known manner with an ion beam. The underside
of the sample 1 is already cut loose, and the sample is only
connected to the wafer 2 via the connection 7 between wafer 2 and
sample 1. The sample 1 nowadays has dimensions of the order of
magnitude of 10 .mu.m (i.e. length perpendicular to the line AA')
at a thickness (i.e. dimension in the direction of the line AA') of
100 nm. The wafer 2 nowadays has a diameter of 300 mm, and it
should be possible to take the sample from any random location on
the wafer. FIG. 1B shows a transverse cross-section according to
the line AA' depicted in FIG. 1A, in which it can clearly be seen
that the underside of sample 1 is free from the wafer 2.
FIG. 2 schematically shows a manipulator system 5, consisting of a
manipulator 4 and a sample carrier 3. The manipulator 4 is able to
move the sample carrier 3 within the plane of the wafer 2 to the
position of the sample 1 to be removed from the wafer 2 (see FIG.
1A) and also perpendicular thereto. In view of the dimensions of
the sample 1, this will have to occur with an accuracy of the order
of magnitude of 1 .mu.m. Manipulators for positioning wafers with
this type of accuracy are known per se.
FIG. 3 schematically shows an extremity of the sample carrier 3
(see FIG. 2), which is connected to the manipulator 4 (see FIG. 2)
and which is attached to the sample 1, whereby the connection 6 is
embodied in the form of a metal deposition. After cutting loose the
connection 7 between the sample 1 and the wafer 2 with a particle
beam, the sample 1 is only carried by the sample carrier 3.
FIG. 4 schematically shows the manipulator 4, which is positioning
the sample carrier 3 (connected thereto)--and the sample 1 attached
thereto--above a TEM grid 14. The sample carrier 3 is positioned
above the TEM grid 14 by the manipulator 4 in such a manner that
the sample 1, after separation, is located entirely within one of
the hollows of the TEM grid 14 and the sample carrier 3 comes to
rest upon one or more of the bars of the TEM grid 14, such as is
further depicted in FIG. 5. Subsequently--using, for example, a
laser or particle beam--a separation is applied between the
manipulator 4 and the sample carrier 3 at a position 8, whereby the
portion of the sample carrier 3 that protrudes with respect to the
sample 1 and that remains connected to the sample 1 is large with
respect to the sample 1.
FIG. 5 schematically shows the positioning of the sample 1 after a
separation has been applied between the sample carrier 3 and the
manipulator 4. The sample carrier 3 rests upon one bar of the TEM
grid 14 and the sample 1 is located entirely within a hollow 17 of
the TEM grid 14, as a result of which the sample 1 is easily
accessible for the purpose of processing and/or analysis in other
apparatus.
FIG. 6 schematically shows an embodiment of the manipulator system
5, whereby the sample carrier 3 (see FIG. 2) is formed by the end
portion 9 of a supply 11 of wire. In addition, separation means 15
are schematically shown here, which means 15 may be mechanical in
nature--as will be explained further in FIG. 7--but which may also
be embodied as severing means that perform the separation with the
aid of a laser or particle beam. Use of the supply 11 of wire makes
it possible, in the case of repeated application of the method, to
produce sample carriers 3 in a simple manner. The sample carrier 3,
and thus the wire from which the sample carrier 3 is formed, should
be very thin, in view of the dimensions of the sample 1 upon which
the sample carrier 3 is positioned. In this context, one might
consider wire such as that used in the semiconductor industry for
"bonding" chips, which wire can have a diameter nowadays of 10
.mu.m.
FIG. 7A schematically shows an embodiment of the mechanical
separation means referred to with regard to FIG. 6, whereby the end
portion 9 is mechanically severed from the supply 11 of wire using
knives 16 operating toward one another.
FIG. 7B schematically shows an embodiment of the mechanical
separation means referred to with regard to FIG. 6, whereby the end
portion 9 is mechanically severed from the supply 11 of wire by
means of stretching of the supply 11 of wire, achieved by moving
apart the clamps 12, as a result of which constriction of the wire
of the supply 11 of wire occurs. The constriction will have a
diameter much smaller than the diameter of the end portion 9, so
that the needle-like extremity of the end portion 9 to be newly
formed as a result of this constriction will also be much thinner
than the diameter of the wire of the supply 11 of wire, so that
positioning upon the microscopic sample 1 is facilitated.
FIG. 8 shows--in a front elevation and also in a transverse
cross-section according to line AA'--a sample carrier 3 that can be
detachably coupled to the manipulator 4 already shown in FIG. 2. In
the figure, it can be seen that the sample carrier 3 is formed from
a relatively thick body 18, which the manipulator 4 can grip for
the purpose of coupling, and tapering fingers 19 for attachment of
samples 1. The form of the sample carrier 3 is chosen in such a
manner that it is possible to use it in standard specimen carriers
in apparatus in which processing and/or analysis are performed.
These may be specimen carriers for use with TEM grids for
application in TEM apparatus. The sample carrier 3 is embodied to
carry several samples 1, thanks to the presence of several fingers
19. As a result of the form, placement and direction of the fingers
19, one achieves a situation whereby a sample 1 can be attached to
the extremity of one of the fingers 19 without the risk that a
sample 1 that is already attached to another finger 19 will come
into contact with the wafer 2, seeing as such contact could damage
the sample 1 that is already attached, or could damage the
connection between the sample carrier 3 and the sample 1 that is
already attached. In addition, sample carrier 3 is provided with a
(unique) identification code 13, which, during subsequent analyses
and/or processing, facilitates identification of the samples
attached to the sample carrier 3. This identification is of
particular advantage in environments in which large numbers of
samples are analyzed, such as in environments for the production of
integrated circuits.
FIG. 8B schematically shows a sample carrier 3 such as shown in
FIG. 8A, which is coupled to a manipulator 4 with the aid of a
coupling mechanism 10, which coupling mechanism 10 is part of the
manipulator 4. The mouth of this coupling mechanism 10 is closed
using an actuator that is not depicted, whereby the sample carrier
3 becomes clamped.
FIG. 9 schematically shows another embodiment of a detachable
sample carrier 3, which, in turn, is attached to a flat holder with
one or more hollows 17--such as a TEM grid 14--such as is further
depicted in FIG. 10. This sample carrier 3 has a U form with a
relatively thick middle portion 20 and thin legs 21. The relatively
thick middle portion 20 can be gripped by a coupling mechanism 10
such as that shown in FIG. 8B. The sample 1 is attached to the thin
legs 21.
FIG. 10 schematically shows the sample carrier 3 such as shown in
FIG. 9 attached to a flat holder in the form of a TEM grid 14 with
hollows 17, whereby the samples 1 connected to the sample carrier 3
both lie freely within a hollow 17. In addition, the TEM grid 14 is
provided with a unique identification code 13.
* * * * *